This invention generally relates to electronic displays and more specifically to electronic displays addressed by organic-based field effect transistors.
Microencapsulated, particle-based displays can be made highly reflective, bistable, and optically and electrically efficient. To obtain a high resolution display, however, individual pixels of a display must be addressable without interference from adjacent pixels. One way to achieve this objective is to provide an array of nonlinear transistor elements, where one transistor is associated with each pixel. The addressing electrodes are connected to the pixel through the transistor.
Most examples of nonlinear elements to date have been fabricated using vacuum-deposited silicon on glass. This process is costly in addition to being complex. The complexity prevents large area devices from being readily constructed. In addition, it is difficult to create silicon transistors on plastic or other flexible film.
Recently, there has been significant development in the area of organic semiconducting polymers and molecules. Thin film transistors have been made out of semiconducting polymers. See Bao et al., Soluble and Processable Regioregular Poly(3-hexylthiophene) for Thin Film Field-Effector Transistor Applications with High Mobility, Appl. Phys. Lett. 69(26), 4108 (December 1996); and Bao et al., High-Performance Plastic Transistors Fabricated by Printing Techniques, Chem. Mater. 1997, 9, 1299. U.S. Pat. No. 5,574,291 describes addressing liquid crystal displays with transistors made out of semiconducting polymers. While remarkable advances have been made in the performance of organic-based transistors, the mobility characteristics of many organic semiconductor materials and devices are insufficient to successfully drive many types of liquid crystal or emissive displays. Therefore, many organic-based transistors are not suitable for use with liquid crystal displays.
In addition, liquid crystals can degrade the transistors when they come in contact with the transistors. Many organic semiconductor materials can be swollen by, or dissolved by, liquid crystalline fluids because those fluids are good solvents. This solvent compatibility makes it challenging to design systems in which organic transistor devices can remain stable while in contact with or close proximity to liquid crystalline solvents, limiting their viability.
In one aspect, the invention features a display. The display comprises an encapsulated display media and an organic-based field effect transistor. The display media comprises a plurality of particles and a fluid, the display media has a first surface and a second surface. The organic-based field effect transistor comprises an organic semiconductor. The organic-based field effect transistor is disposed adjacent the second surface of the display media for addressing the display media. The display media can comprise a plurality of microencapsulated electrophoretic particles, suspended particles, or rotating balls.
In one embodiment, the organic semiconductor of the transistor comprises a polymeric and/or oligomeric semiconductor. For example, the polymeric semiconductor can comprise polythiophene, poly(3-alkyl)thiophene, alkyl-substituted oligothiophene, polythienylenevinylene, or poly(para-phenylenevinylene). For example, the oligomeric semiconductor can comprise alpha-hexathienylene. In another embodiment, the organic semiconductor can be selected from a group consisting of pentacene, phthalocyanine, benzodithiophene, fullerene, buckminsterfullerene, tetracyanonaphthoquinone, and tetrakisimethylanimoethylene, and derivatives.
In one embodiment, the display further comprises a barrier layer disposed adjacent at least a portion of the organic-based field effect transistor. In one detailed embodiment, the display comprises a plurality of pixel electrodes disposed adjacent the second surface of the display media and an array of transistors, each transistor protected with a barrier layer disposed adjacent the transistor. In another detailed embodiment, the display comprises an array of transistors encapsulated in a barrier capsule and disposed adjacent the second surface of the display media such that each transistor is connected to a pixel electrode.
The barrier layer or capsule can comprise a metal film, a metal oxide coating, a polymeric coating or a combination of these materials. In particular, a barrier layer or capsule comprising a metal film will also comprise an insulating coating to prevent unwanted electrical connections between the barrier capsule or layer and the transistor. The barrier layer or capsule can protect the transistor from light such as visible light or ultraviolet light. The barrier layer or capsule can protect the transistor from oxygen or moisture. In addition, the barrier layer or capsule can protect the transistor from solvents or other chemicals. In another embodiment, the organic-based field effect transistors are disposed on a substrate. The substrate can be opaque. The substrate can protect the transistors from oxygen or moisture.
In another aspect, the invention features a method of manufacturing a display. The method comprises the steps of: (a) providing an encapsulated display media comprising a plurality of particles and a fluid, the display media having a first surface and a second surface; and (b) providing an organic-based field effect transistor array comprising an organic semiconductor adjacent the second surface of the display media.
In one embodiment, step a) comprises providing an encapsulated display media on a first substrate; and step b) comprises (b1) providing an organic-based field effect transistor array on a second substrate, and (b2) combining the display media and the organic-based field effect transistor array to form the display.
In one embodiment, step (b) comprises printing the organic-based field effect transistor array. In one detailed embodiment, step (b) comprises printing the organic-based field effect transistor array using a solvent assisted printing step. In one embodiment, step (a) comprises providing a display media comprising microencapsulated electrophoretic particles, suspended particles, or rotating balls.
In another embodiment, step (b) comprises providing an organic-based field effect transistor array comprising a polymeric or oligomeric semiconductor. For example, the polymeric semiconductor can comprise polythiophene, poly(3-alkyl)thiophene, alkyl-substituted oligothiophene, polythienylenevinylene, or poly(para-phenylenevinylene). For example, the oligomeric semiconductor can comprise alpha-hexathienylene. In another embodiment, the organic semiconductor is selected from a group consisting of pentacene, phthalocyanine, benzodithiophene, fullerene, buckminsterfullerene, tetracyanonaphthoquinone, and tetrakisimethylanimoethylene.
In another embodiment, step (b) comprises (b1) providing an organic-based field effect transistor array, and (b2) providing a barrier layer over each organic-based field effect transistor of the array to protect the transistor. In another embodiment, step (a) comprises (a1) providing a display media and (a2) providing a plurality of pixel electrodes adjacent the second surface of the display media; and step (b) comprises (b1) encapsulating the transistor array in a barrier capsule and step (b2) disposing the encapsulated transistor array adjacent the display media such that each transistor is disposed adjacent a pixel electrode. The barrier layer or capsule can comprise a metal film, a metal oxide coating, or a polymeric coating. The barrier layer or capsule can protect the transistor from light such as visible light or ultraviolet light. The barrier layer or capsule can protect the transistor from oxygen or moisture. The barrier layer or capsule can further protect the transistor from a solvent.
In another embodiment, step (b) comprises providing an organic transistor array by evaporating the organic semiconductor. In another embodiment, step (b) comprises providing an organic transistor array by solvent coating an insulator of the transistors. In still another embodiment, step (b) comprises providing an organic transistor array by evaporating conductive leads to the transistors.